I can try :)
Basically, when you are doing something like this, the Linksys is doing what
Cisco would call 'overloading'.
It is really PAT... Each computer that goes out of the Linksys is given a
different port number.
The router (in this case the Linksys) will save the non-routable IP address
(192.16.x.x) and the port it went out on in an 'address translation table'.
After it has the info, the router will replace the computer's non-routable
IP address with it's routable IP address. The router also replaces the
sending computer's source port with the port number that matches where the
router saved the sending computer's address information in the address
translation table. This means the translation table has a mapping of the
computer's non-routable IP address and port number along with the router's
IP address.
When a packet comes back into the network, the router checks the destination
port on the packet. It then looks in the address translation table to see
which computer on the internal network the packet belongs to. It changes
the destination address and destination port to the ones saved in the
address translation table and sends it to that computer.
Since the NAT router now has the computer's source address and source port
saved to the address translation table, it will continue to use that same
port number for the duration of the connection. A timer is reset each time
the router accesses an entry in the table. If the entry is not accessed
again before the timer expires, the entry is removed from the table.
And that is really how it works :-)
So, I was really not giving you the whole story when I mentioned
encapsulation.
Hope this helped...
Regards,
-----Original Message-----
From: Sivaramakrishna Iyer Krishnan
[mailto:krishnan@xxxxxxxxxxxxxxxxxxxxxx]
Sent: Monday, July 01, 2002 2:51 PM
To: Marshal Schoener
Cc: associate@xxxxxxxxxxxxxx
Subject: Re: question about networks [1:9870]
Hi,
Can you explain a little more. The hardware address keeps changing on
every hop. So, which layer is this data encapsulated. Is it stored as
part of the data itself ?. I am still not clear.
thanks,
Krishnan.
Marshal Schoener wrote:
>
> It is very basic address translation.
> All the packets sent out are first encapsulated with all the information
> they need...
> Good luck,
>
> -----Original Message-----
> From: Sivaramakrishna Iyer Krishnan
> [mailto:krishnan@xxxxxxxxxxxxxxxxxxxxxx]
> Sent: Monday, July 01, 2002 2:33 PM
> To: associate@xxxxxxxxxxxxxx
> Subject: question about networks [1:9870]
>
> Hi all,
>
> I have a private network set up at home. I have a linksys router that I
> connect my cable modem to and have 2 PCs connected to the linksys
> router. Now, I have a one way cable but that should not affect my
> question.
>
> When I connect to the internet my linksys router is given an IP address
> from the cable(ISP). Say this is u.v.w.x. Although the PCs that are
> connected to the linksys router have IP address 192.168.x.y (private
> addresses). Now, I am able to access the internet using both the PCs.
> Say for example, I am doing a http request, how does it know that the
> reply needs to be send to me. It cannot send the source address
> 192.168.x.y as that is private to my network. So, it should be taking
> the IP address that the cable modem provides it and sending out the
> request, then when it gets the response how does the router know which
> PC to send the response to.
>
> Is the question clear or am I missing something very trivial.
>
> thanks,
> Krishnan.
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